Photoresponsive imaging members with protective copolyurethane overcoatings

ABSTRACT

An imaging member comprised of a photoconductive layer, and a protective copolyurethane overcoating of the formula   &lt;IMAGE&gt;  +TR &lt;IMAGE&gt;  wherein A is a trivalent group; A&#39; is a bivalent group; R is selected from the group consisting of alkylene, substituted alkylene, arylene, and substituted arylene; x and y are number mole fractions of from about 0.05 to about 0.95 subsequent to the provision that the sum of x+y is equal to 1.0. Also disclosed are processes for the preparation of the aforementioned copolyurethanes.

This is a division, of application Ser. No. 150,871, filed Feb. 1, 1988,now U.S. Pat. No. 4,820,601.

BACKGROUND OF THE INVENTION

This invention is generally directed to imaging members, and morespecifically the present invention relates to the selection of certainnovel polyurethanes which function as protective overcoatings forphotoresponsive imaging members, especially inorganic imaging members.In one embodiment, the present invention relates to an imaging membercomprised of an inorganic photoconductive composition, and coatedthereover certain polyurethane polymers. Also, in another embodiment ofthe present invention, there are provided imaging members comprised of aphotogenerating layer, a hole transport layer, and thereover as aprotective overcoating specific polyurethane polymers. Theaforementioned imaging members are useful in electrophotographicprinting and imaging processes, and in particular, can be selected forthe generation of latent images in electrostatic imaging systems.

The polyurethanes of the present invention, when selected for theimaging members disclosed herein, perform a variety of functionsinclusive of providing protection for the aforementioned members fromabrasive, physical, and chemical contamination. Accordingly, thus forexample, the specific overcoating polyurethanes of the present inventionpermit the resulting imaging member to be resistant to ozone and otherchemical substances produced by corona charging devices. Also, thepolyurethane overcoatings of the present invention substantiallyeliminate undersirable scratching of the imaging members involved, andfurther these coatings can function as release materials permitting theexcellent removal and transfer of toner images. Furthermore, thepolyurethane coatings of the present invention can be easily formulatedas discrete layers and remain essentially nonreactive to the ink/solventformulations utilized for certain liquid ink xerographic developmentprocesses. Moreover, the protective overcoatings of the presentinvention are nontoxic and are, therefore, inert to users of the device.Additionally, the protective polyurethane overcoatings are not sensitiveto changes in many environmental conditions (humidity and temperature),thus ensuring the electrical performance of the protected imagingmembers for numerous imaging cycles.

It is known that the application of protective coatings to certainphotoconductive materials, particularly inorganic photoconductivematerials, is designed primarily for the purpose of extending the usefullife of the resulting devices. Generally, for these coatings to providethe desired protection they should possess certain mechanicalproperties, and are usually applied in a substantially uniformthickness. Additionally, the coating material should be selected so asto not adversely effect the photoelectric properties of thephotoreceptor, for example, the coating should not appreciably injectcharges in the dark. The protective coatings should also not conductlaterally on the overcoated surface thereof. Further, in someappllications the coating must be transparent, and possess a darkresistivity at least equal to the dark resistivity of thephotoconductive material. For example, photoconductive materials such asselenium have a resistivity in the dark of 10¹⁰ to 10¹² ohm-cm, thus thedark resistivity of the protective coating should usually be in thisrange when it is used as a protectant for selenium. In addition, thecoatings should not be sensitive to changes in humidity and certaintemperature ranges otherwise the photoelectric properties of theprotected photoreceptors can be altered.

With regard to vitreous selenium, one of the most widely usedphotoconductive materials, it suffers from two serious defects, namely,its spectral response is somewhat toward the blue or near ultraviolet,and the preparation of uniform films of vitreous selenium has requiredhighly complex processes wherein critical parameters are involved.Accordingly, from a commercial economic aspect, it is important thatxerographic selenium devices be utilized for numerous imaging cycles.The overcoatings of the present invention enable this and otherobjectives to be achieved.

Deterioration by mechanical abrasion attendant to the developing and thecleaning processes, wherein in one cleaning process a rapidly rotatingbrush contacts the photoconductive surface for the purpose of removingtherefrom any residual developer particles adhering thereto subsequentto the transfer step, has been observed in selenium. In addition tomechanical abrasion, the selenium photoreceptor may be subjected tointense heat, which over a period of time adversely effects itsphotoconductivity. Accordingly, and for other reasons inclusive ofpreventing crystallization of selenium upon exposure to chemical vapors,various protective coatings, or overcoatings have been applied toselenium devices. Thus, there is described in U.S. Pat. No. 3,397,982 anelectrostatic member comprised of a photoconductive layer including aninorganic glass material, and thereover an overcoating comprised ofvarious oxides, such as germanium oxides, the oxides of vanadium, andsilicon dioxide.

Additionally, in U.S. Pat. No. 2,886,434 there are disclosed processesfor the protection of selenium photoconductive substances with a thintransparent film of a material having electrical characteristics equalto selenium. Examples of materials disclosed in the '434 patent as aprotective layer for selenium include zinc sulfide, silica, varioussilicates, alkaline earth fluorides, and the like. Furthermore, there isdisclosed in U.S. Pat. No. 2,879,360 a photoconductor comprising asupport substrate, a layer of photoconductive material, and as aprotectant a thin film of silicon dioxide superimposed upon thephotoconductive layer.

Also, there are illustrated in the prior art photoresponsive devicescomprised of a conductive substrate overcoated with a hole injectinglayer, which in turn is overcoated with a hole transport layer, followedby a carrier generating layer, and an insulating organic resin as a topcoating. These devices have been found to be very useful in variousimaging systems, and have the advantage that high quality images areobtained with the overcoating acting primarily as a protectant. Anothersimilar overcoated photoresponsive device is comprised of a conductivesubstrate layer, a generating layer, and a transport layer. In suchdevices, the generating layer can be overcoated on the transport layer,or the transport layer may be overcoated on the generating layer.Examples of such devices are described in U.S. Pat. No. 4,265,990, thedisclosure of which is totally incorporated herein by reference.

Additionally, there are illustrated in U.S. Pat. No. 4,423,131, thedisclosure of which is totally incorporated herein by reference,entitled Photoresponsive Devices Containing Polyvinylsilicate Coatings,improved photoresponsive imaging members with a protective overcoatingtop layer of a crosslinked polyvinylsilicate resulting from the reactionof polysilicic acid with a polyvinyl alcohol with a number averagemolecular weight of from about 10,000 to about 100,000.

Several of the above-described overcoated organic photoresponsivedevices are not effectively protected after extended usage, and in someinstances the imaging properties thereof are adversely effectedsubsequent to a few imaging cycles. More specifically, with thesedevices the properties of the top overcoating material, or theproperties of the other layers are usually adversely effected by ozoneand other contaminants present in the environment by the developingcompositions which contact the photoresponsive device for the purpose ofrendering the image visible, and mechanical abrasion during cycling.Accordingly, images of low quality, or no images whatsoever are produceddepending upon the extensiveness of the damage caused to the layers ofthe photoconductive device selected. Furthermore, in some instances, thetoner materials employed do not sufficiently release from thephotoresponsive surface, leaving unwanted toner particles thereoncausing them to be subsequently embedded into, or transferred from theimaging surface in later imaging steps thereby resulting in undesirableimages of low quality and/or high background. Also, in some instances,the dried toner particles adhere to the imaging member and print out asbackground areas. This can be particularly troublesome when knownsilicone resins or elastomeric polymers are employed as overcoatingmaterials for their melted toner release characteristics since any lowmolecular weight components contained in these polymers can migrate tothe surface of the silicone polymer layer, and act as an adhesive fordry toner particles brought in contact therewith during imagedevelopment. There thus results undesirable high background areas in thefinal image since toner particles together with the developed images areeffectively transferred to the receiving sheet.

Furthermore, illustrated in U.S. Pat. No. 4,562,132, the disclosure ofwhich is totally incorporated herein by reference, entitledPhotoresponsive Imaging Members Containing Electron TransportOvercoatings, are imaging members comprised of a supporting substrate, ahole transport layer comprised of an arylamine hole transportingcompound dispersed in an inactive resinous binder, a photogeneratinglayer comprised of a photogenerating pigment optionally dispersed in aresinous binder, and as a protective topcoating an electron transportingcompound of the following formula dispersed in a resinous binder##STR2## where X is cyano or alkoxycarbonyl groups, A and B are electronwithdrawing groups, m is a number of from 0 to 2, n is the number 0 or1, and W is an electron withdrawing group selected from the groupconsisting of acyl (COR), alkoxycarbonyl (COOR), alkylaminocarbonyl(CONHR), and derivatives thereof.

Moreover, illustrated in U.S. Pat. No. 4,835,081, entitled PhoresponsiveImaging Members With Electron Transport Overcoatings, the disclosure ofwhich is totally incorporated herein by reference, are imaging memberssimilar to those of the present application with the exception thatthere is selected for the overcoating of imaging members of the presentinvention certain novel copolyurethane overcoatings. More specifically,there are described in this patent inorganic photoresponsive imagingmembers having incorporated therein as protective overcoatings electrontransporting polycondensation polymers derived from the polycondensationof 2,2-bis(hydroxymethyl)butyl9-dicyanomethylene-fluorene-4-carboxylate, and diisocyanate. Alsodisclosed in the copending application are layered photoresponsiveimaging members comprised of a supporting substrate, a photoconductivelayer, an arylamine hole transport layer, and a protective electrontransporting overcoating layer comprised of the aforementionedpolyurethane polymers. In addition, the electron transport polyurethanepolymers of the patent are useful as the top overcoating forpositive-charging layered photoresponsive devices comprised of asupporting substrate, a hole transport layer, and a photoconductivelayer, and wherein the polymers are of the following formula. ##STR3##wherein A is a trivalent linkage; B is a functional group such as anester (--OCO--), a carbonate (--OCOO--) or a carbamate (--OCONH--); R isa bivalent group, and n represents a certain nunmber of repeating units.

The copolyurethane overcoatings of the present invention are somewhatsimilar to the aforementioned polyurethane coatings, and further theaforementioned copolyurethanes have enhanced flexibility characteristicsas compared to those polyurethanes illustrated in the '132 patent. Morespecifically, the copolyurethanes of the present invention containtherein certain highly flexible segments enhancing its flexibilitycharacteristics which is of particular importance when these polymersare selected as protective overcoatings for belt photoconductors, andmoreover the copolyurethanes of the present invention are useful as aprotectant for extended time periods. Furthermore, the presence of thesoft flexible segments in the copolyurethanes of the present inventiongreatly improve their solubilities in common coating solvents such asaromatic hydrocarbons, tetrahydrofuran, chlorinated chydrocarbons, andthe like, thereby enabling the coating process to be accomplished in avariety of solvents by different coating techniques, such as dipcoating, spray coating, and the like. More importantly, theincorporation of the flexible segments into the polyurethane structurerenders the synthesis of higher molecular-weight polyurethanes feasible,thus affording tough, highly durable polyurethanes for protectiveovercoating application.

Other prior art includes U.S. Pat. Nos. 4,474,865, which describesimproved photoresponsive imaging members with electron transportingcomponents containing specific dicyano fluoro ester moieties; 3,928,034,which illustrates the incorporation of electron transporting moietieschemically attached to polymers, reference columns 7 and 8; and4,007,043; 4,063,947; 4,075,012; and 3,896,184. Also of interest areU.S. Pat. Nos. 3,108,092; 3,451,969; 4,063,947; and 4,203,764; andHolland Patent Publication 7606525. Of particular interest are U.S. Pat.No. 4,063,947 and Holland 7606525, which disclose imaging members withelectron transport compounds, reference column 3, line 57, to column 4,line 30, of the '947 patent.

While the above-described imaging members disclosed, particularly thoseof the pending application, are suitable for their intended purposes,there continues to be a need for improved protective overcoatings forincorporation into inorganic and organic imaging members. Morespecifically, there continues to be a need for protective overcoatingsfor inorganic imaging members, inclusive of selenium, and seleniumalloys, which simultaneously function as charge transporting componentsenabling the resulting photoresponsive imaging members to be useful inxerographic imaging processes. Additionally, there continues to be aneed for overcoatings which possess excellent toner release properties,and are impermeable to chemical materials produced by corona chargingdevices, and wherein the overcoatings selected are soluble in a varietyof solvents thereby permitting improved coatability, and allowingeconomical spray and dip coating processes to be selected. There alsocontinues to be a need for insulating protective overcoatings which arenot conductive to charges applied by a corona charging device.Furthermore, there remains a need for protective overcoatings which aremechanically strong and durable while simultaneously being insensitiveto the effect of humidity. Also, there is a need for heat resistantovercoatings for inorganic photoresponsive imaging members which arecapable of protecting these members from direct exposure to heat withoutadversely effecting their imaging performance. There also remains a needfor protective overcoatings which prevent the escape of toxic materials,especially inorganic materials such as arsenic and tellurium fromphotoreceptor imaging members. Moreover, there is a need for protectiveovercoatings that will prevent photoconductors such as selenium fromcrystallization upon exposure to chemical vapors. Further, therecontinues to be a need for new protective overcoatings for inorganicphotoconductive members inclusive of members comprised of selenium andselenium alloys. Also, there is a need for reliable single componentprotective overcoatings for layered imaging members, which coatings haveseveral desirable characteristics including toughness and highdurability.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedphotoresponsive imaging member with many of the above noted advantages.

In a further object of the present invention there are providedcopolyurethane overcoatings for photoresponsive imaging members, whichovercoatings are chemical, heat and abrasion resistant.

In another object of the present invention there are provided inorganicphotoresponsive imaging members with a photogenerating composition, andcoated thereover as a protective overcoating certain mechanically strongcopolyurethanes.

In yet a further object of the present invention there are providedlayered photoresponsive imaging members containing as top protectiveovercoatings specific copolyurethanes, which overcoatings are insulatingand not conductive or leaky to charges applied by a corona chargingdevice.

In still another object of the present invention there are providedphotoresponsive imaging members, inclusive of those comprised ofselenium and selenium alloys, with protective overcoatingcopolyurethanes, which members are useful for generating electrostaticlatent images, particularly colored images in xerographic imaging orprinting processes.

Another object of the present invention resides in the provision ofhumidity insensitive copolyurethane overcoatings for inorganicphotoresponsive imaging members.

Additionally, another object of the present invention resides in theprovision of single component polymeric overcoatings for photoreceptors,which overcoatings are environmentally safe, and are inert to the usersof the devices.

Furthermore, in another object of the present invention there areprovided novel copolyurethanes, which may be selected as protectiveovercoatings for imaging members, which copolyurethanes are soluble in avariety of different solvents permitting improved coatability, andallowing the utilization of spray or dip coating processes.

Moreover, in another object of the present invention there are providedinorganic photoconductive imaging members, inclusive of those comprisedof selenium and selenium alloys, with the protective copolyurethaneovercoatings illustrated herein, which members can be utilized for anextended number of imaging cycles exceeding, for example 50,000.

These and other objects of the present invention are accomplished by theprovision of photoresponsive imaging members having incorporated thereinas protective overcoatings certain novel copolyurethanes. Morespecifically, in one embodiment of the present invention there areprovided inorganic photoresponsive imaging members having incorporatedtherein as protective overcoatings certain novel copolyurethanes of theformula ##STR4## wherein A is a trivalent group such as dimethylenealkyl group, or triethylene amine; A' is a bivalent group such asalkylene, arylene, polyether segments, and the derivatives thereof; R isselected from the group consisting of alkylene, arylene, and thederivatives thereof; x and y are number mole fractions of from about0.05 to about 0.95 such that x+y=1.0.

Examples of copolyurethanes selected as protective overcoatings includethose as represented by the following Formulas I, II and III: ##STR5##wherein A is a trivalent group; R is a bivalent group such as alkylene,arylene, substituted alkylene or substituted arylene group such asmethylene, dimethylene, trimethylene, tetramethylene, phenylene,tolylene, and the like; R' is an alkyl, or substituted alkylsubstituent, an aryl or substituted aryl substituent; x and y representnumber mole fractions of from 0.05 to about 0.95 such that x+y=1.0; andm and n are positive integers of from 1 to about 20. Examples of alkylsubstituents include those with from about 1 to about 25 carbon atoms,such as methyl, ehtyl, propyl, butyl, pentyl, dodecyl, and the like;while examples of aryl substituents are those with from about 6 to about24 carbon atoms, such as phenyl and naphthyl.

Specifically, examples of copolyurethane overcoating polymers selectedfor the imaging members illustrated herein include those represented bythe formulas illustrated in FIGS. 1 to 10, wherein the substituents suchas x and y are as defined herein.

The copolyurethanes of the present invention can be synthesized,reference Reaction Scheme 1 that follows, by the reaction of thedihydroxy-functionalized monomer (1a) and a diol (2) such as ethyleneglycol, diethylene glycol, octanediol, and the like, with a slightexcess of diisocyanate (3) in an inert reaction solvent medium at atemperature usually below 100° C., and preferably between 50° C. to 85°C. In general, a suitable catalyst such as tertiary amines, dibutyltindiacetate or dibutyltin dilaurate is employed to increase the rate ofpolymerization. ##STR6##

Examples of suitable solvents for the above polymerization reactioninclude ethyl acetate, tetrahydrofuran, dioxane, dimethyl sulfoxide,dimethyl acetamide, and dimethylformamide. Also, the aforesaid reactionis generally accomplished in a period of from about 2 to about 24 hoursdepending on the nature of the reagents and reaction conditions.

Examples of diisocyanates that may be selected for the preparation ofprotective overcoating copolyurethanes include methane diisocyanate,1,2-ethane diisocyanate, 1,3-propane diisocyanate, 1,6-hexanediisocyanate, 1,4-cyclohexane diisocyanate, 1,4-dimethylenecyclohexanediisocyanate, benzene diisocyanate, toluene diisocyanates, methylenebis(4-phenyl isocyanate), and the like.

Specific examples of the dihyroxy-functionalized monomer (1a) selectedfor the preparation include ##STR7##2,2-bis(hydroxymethyl)butyl9-dicyanomethylenefluorene-4-carboxylate;##STR8## 3,5-dihydroxyphenyl9-dicyanomethylenefluorene-4-carboxylate;##STR9## 2-[bis(2-hydroxyethyl)amino]ethyl9-dicyanomethylenefluorene-4-carboxylate; ##STR10##3-hydroxy-2-nitro-2-hydroxymethylpropyl9-dicyanomethylenefluorene-4-carboxylate; ##STR11##2,3-dihydroxypropyl9-dicyanomethyleneluorene-4-carboxylate; ##STR12##2-[bis(2-hydroxyethyl)amino]ethyl9-dicyanomethylenefluorene-4-carboxylate; and ##STR13##2,2-bis(hydroxymethyl)propyl9-dicyanomethylenefluorene-4-carboxylate.

The protective overcoating copolyurethanes illustrated herein andformulated in accordance with the processes of the present invention canbe characterized by various analytical techniques includingspectroscopy, GPC, vapor pressure osmometry, and the like. Also, thecopolyurethane overcoatings are applied to the imaging members disclosedhereinafter in a thickness that will enable the objectives of thepresent invention to be achieved. Generally, the thickness of this layeris from about 0.1 micron to about 10 microns, and preferably from about1 micron to about 5 microns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be illustrated with reference to specificpreferred embodiments wherein

FIGS. 1 through 10 are formulas representing protective overcoatingcopolyurethanes;

FIG. 11 represents a cross-sectional view of a photoresponsive imagingmember of the present invention;

FIG. 12 represents a cross-sectional view of a preferred photoresponsiveimaging member of the present invention;

FIG. 13 represents a cross-sectional view of a preferred photoresponsiveimaging member of the present invention; and

FIG. 14 represents line graphs for two photoresponsive imaging members.

There is illustrated in FIG. 11 a photoresponsive imaging member of thepresent invention comprised of a supporting substrate 1, aphotoconductive layer 3, and as a protective overcoating 5, thecopolyurethanes illustrated herein.

Illustrated in FIG. 12 is a preferred photoresponsive imaging member ofthe present invention comprised of an aluminum supporting substrate 15,a selenium or selenium arsenic alloy photoconductive layer 17, and a topovercoating layer 19 comprised of the copolyurethane of FIG. 3illustrated herein, and derived from the polycondensation of2,2-bis(hydroxymethyl)butyl 9-dicyanomethylenefluorene-4-carboxylate andt-butyl bis(2-hydroxyethyl)amine with toluene diisocyanates.

Illustrated in FIG. 13 are positively charged layered photoresponsiveimaging members comprised of a supporting substrate 30, an aryl aminehole transport layer 33, comprised of a diamine 34 such asN,N'-diphenyl-N,N'-bis(3-methyl phenyl) 1,1'-biphenyl-4,4'-diaminedispersed in an inactive resinous binder 35, a photogenerating layer 37in contact therewith, optionally dispersed in a resinous binder 39, anda copolyurethane top overcoating layer 41 comprised of thecopolyurethane of FIG. 1 illustrated herein.

With reference to FIG. 14, the solid line represents a photoinduceddischarge curve for the photoresponsive member of FIG. 12 while thedotted line is a photoinduced discharge curve for the samephotoresponsive member (control) with no copolyurethane overcoatingthereon.

With further reference to the photoresponsive imaging membersillustrated herein, and particularly with reference to FIGS. 11 to 13,the substrates layers may be comprised of any suitable material havingthe requisite mechanical properties. Thus, the substrate layers may becomprised of a layer of conductive materials such as metallized organicpolymeric materials, or inorganic materials such as, for example,aluminum, chromium, nickel, brass, or the like. The substrate may beflexible or rigid, and may be of a number of many differentconfigurations, such as, for example, a plate, a cylindrical drum, ascroll, an endless flexible belt, and the like. Preferably, thesubstrate is in the form of an endless flexible belt or a rigid drum.

Further, the photoconductive layers of FIGS. 11 and 12 can be comprisedof known photoconductive materials including, for example, amorphousselenium, amorphous selenium alloys, halogen-doped amorphous selenium,halogen-doped amorphous selenium alloys, trigonal selenium, selenide andcarbonates with trigonal selenium, reference U.S. Pat. Nos. 4,232,102and 4,233,283, the disclosures of which are totally incorporated hereinby reference; cadmium sulfide, cadmium selenide, cadmium telluride,cadmium sulfur selenide, cadmium sulfur telluride, cadmium selenotelluride, copper and chlorine-doped cadmium sulfide, and the like.Alloys of selenium included within the scope of the present inventionare selenium tellurium alloys, selenium arsenic alloys, seleniumtellurium arsenic alloys, and preferably such alloys containing seleniumin an amount of from about 70 to about 99.5 percent by weight and anoptional halogen material, such as chlorine, in an amount of from about50 to about 200 parts per million.

With respect to FIG. 13, layered photoresponsive imaging members areenvisioned wherein the photogenerating pigment is usually selected fromorganic substances such as vanadyl phthalocyanines, and the holetransport layer is selected from various arylamine molecules asillustrated herein, reference U.S. Pat. No. 4,265,990, the disclosure ofwhich is totally incorporated herein by reference.

The photogenerating components of FIG. 13, generally of a thickness of0.1 to about 5 microns, include metal phthalocyanines, metal-freephthalocyanines, vanadyl phthalocyanines, other known phthalocyanines asdisclosed in U.S. Pat. No. 3,816,118, the disclosure of which is totallyincorporated herein by reference; squarylium pigments, perylenederivatives, and the like. Preferred photogenerating layers includesquarylium pigments, perylene derivatives and vanadyl phthalocyanine.

With reference to FIGS. 11 and 12, the thickness of the substrate layersis generally from about 50 microns to about 5,000 microns, while thethickness of the photoconductive layer is from about 15 microns to about50 microns, and the copolyurethane overcoating is of a thickness of fromabout 0.1 micron to about 10 microns, and preferably is of a thicknessof from about 1 micron to about 5 microns.

Various hole transport layer compositions can be selected providingthese substances are capable of transporting holes, this layer generallyhaving a thickness in the range of from about 5 to about 50 microns, andpreferably from about 20 to about 40 microns. Thus, the transport layercomprises aryl amine molecules of the formula ##STR14## dispersed in ahighly insulating and transparent organic resinous material such aspolycarbonates and the like as illustrated in, for example, the '132patent wherein X is selected from the group consisting of alkyl, andhalogen; preferably methyl and chlorine. The charge transport layer issubstantially nonabsorbing in the spectral region of intended use, thatis, visible light, but is "active" in that it allows injection ofphotogenerated holes from the charge generator layer. Also, the resinbecomes electrically active when it contains from about 10 to 75 weightpercent of the substituted N,N,N',N'-tetraphenylbenzidine correspondingto the foregoing formula. Compounds corresponding to this formulainclude, for example, N,N'-diphenyl-N,N'-bis-(alkylphenyl)benzidinewherein alkyl is selected from the group consisting of methyl, ethyl,propyl, butyl, hexyl, and the like. With halogen substitution, thecompound is N,N'-diphenyl-N,N'bis(halophenyl)benzidine.

Other electrically active small molecules which can be dispersed in theelectrically inactive resin to form a layer which will transport holesinclude triphenylamine, andbis-(4-diethylamino-2-methylphenyl)phenylmethane, andbis(4-diethylaminophenyl)phenylmethane.

Several advantages are associated with the imaging members of thepresent invention inclusive of enabling the generation of images withexcellent resolution, and no background deposits for an extended numberof imaging cycles exceeding, for example 200,000; and moreover, themembers, especially those containing selenium, or selenium alloys willnot crystallize, and are insensitive to humidity. The crystallization ofthe photoconductive materials would have an adverse effect on theirelectrical performance, such as high dark conductivity and high residualpotentials, resulting in poor copy quality such as faint images withhigh backgrounds. Also, the sensitivity of the imaging member tohumidity and temperature would result in the copy quality dependent onthe environmental conditions.

With further respect to the present invention, there are envisionedimaging and printing processes wherein, for example, an electrostaticlatent image is generated on the imaging members illustrated herein,subsequently rendering the image visible with a toner compositioncomprised of toner resin particles such as styrene polymers, pigmentparticles such as carbon black, optional charge enhancing additives suchas cetyl pyridinium chloride, optional external additives such ascolloidal silicas and metal salts, and metal salts of fatty acidsinclusive of zinc stearates; thereafter transferring the developed imageto a suitable substrate such as paper; and permanently affixing theimage thereto by, for example, heat or other similar processes.

The invention will now be described in detail with respect to specificpreferred embodiments thereof, it being understood that these examplesare intended to be illustrative only and the invention is not intendedto be limited to the materials, conditions, and process parametersrecited herein. All percentages and parts are by weight unless otherwiseindicated.

EXAMPLE I Synthesis of 2,2-bis(hydroxymethyl)butyl9-dicyanomethylenefluorene-4-carboxylate (a)

A mixture of 2.1 kilograms of trimethylolpropane, 173 grams offluorenone-4-carboxylic acid, and 8 milliliters of sulfuric acid wasmechanically stirred and heated in a 5-liter flask at 100° C. for 5hours. The mixture was cooled to about 80° C., and 1 liter of methanolwas added. Thereafter, the resulting solution was poured slowly into 17liters of 3 percent aqueous sodium bicarbonate solution with constantstirring, and the crude product resulting was filtered, washed severaltimes with water, and dried. Purification by recrystallization fromethyl acetate afforded 187 grams of pure2,2-bis(hydroxymethylbutyl)fluorenone-4-carboxylate, mp., 134° to 135.5°C.

A solution of 240 grams of the ester as obtained above, 93 grams ofmalononitrile, and 5 milliliters of piperidine in 2.3 liters of absolutemethanol was heated under reflux in a nitrogen atmosphere for 5 hours.After the reaction, the mixture was cooled to about 50° C., and thesolid product was filtered. The product obtained of Formula (a) waswashed twice with methanol, dried in vacuo at 100° C. to afford 229grams of pure (a), mp., 208° to 209° C.

Analysis Calculated for C₂₃ H₂₀ N₂ O₄ : C, 71.12; H, 5.19; N, 7.12.Found: C, 71.23; H, 5.21; N, 7.13.

IR (KBr), cm⁻¹ : 3420; 2230; 1730.

¹ H MNR (DMSO-d₆), ppm: 0.85 (t,3H); 1.4 (q,2H); 3.4 (d, 4H); 4.3 (s,2H); 4.4 (t, 2H); 7.4-8.6 (m, 7H).

EXAMPLE II Synthesis of 3,5-dihydroxyphenyl9-dicyanomethylenefluorene-4-carboxylate (b)

A solution of 30.0 grams of phloroglucinol and 70 milliliters ofpyridine in 300 milliliters of dichloromethane was stirred at roomtemperature under a nitrogen atmosphere. Thereafter, a solution of 8.0grams of (4-chloroformyl-9-fluorenylidene)malononitrile in 400milliliters of dichloromethane was added thereto over a period of 1hour. After addition, the reaction mixture was further stirred foranother hour. The mixture was washed three times dilute aqueous HClsolution, twice with dilute aqueous NaHCO₃ solution, and once withwater. The solution was dried, filtered, and evaporated under reducedpressure to give the crude product. Recrystallization from methanolafforded 6.1 grams of (b), mp., 255.5° to 257° C.

Analysis Calculated for C₂₃ H₁₂ N₂ O₄ : C, 72.63; H, 3.18; N, 7.37.Found: C, 72.41; H, 3.12; N, 7.17.

IR(KBr), cm⁻¹ : 3410; 2230; 1730.

¹ H MNR (acetone-d₆), ppm: 3.25(brs, 2H); 6.8(s,3H); 7.6-9.0(m,7H).

EXAMPLE III Synthesis of 2-[bis(2-hydroxyethyl)amino]ethyl9-dicyanomethylene fluorene-4-carboxylate (c)

A solution of 100.0 grams of triethanolamine and 58 milliliters of drypyridine in 350 milliliters of dry dichloromethane was stirred at roomtemperature under a nitrogen atmosphere. Thereafter, a solution of 8.0grams of (4-chloroformyl-9-fluorenylidene)malononitrile in 400milliliters of dry dichloromethane was added over a period of 1 hour.After addition, the reaction mixture was further stirred for anotherhour. The reaction mixture was washed several times with water to removethe excess and the corresponding hydrochloride salts, dried withanhydrous magnesium sulfate and filtered. Evaporation of the filtrateprovided 5 grams of crude product. Purification by recrystallizationfrom isopropanol afforded 4.5 grams of pure (c), mp., 155.5° to 156.5°C.

Analysis Calculated for C₂₃ H₂₁ N₃ O₄ : C, 68.48; H, 5.25; N, 10.42.Found: C, 68.31; H, 5.33; N, 10.35.

IR(KBr), cm⁻¹ : 3360; 2225; 1730.

¹ H MNR(DMSO-d₆), ppm: 2.6(t,4H); 2.8(t,2H); 3.25(br s, 2H); 3.4(t, 4H);4.4(t, 2H); 7.4-8.6(m, 7H).

Other hydroxy carboxylates can be prepared in a manner similar toExamples I and III.

EXAMPLE IV Synthesis of Copolyurethane (FIG. 1, x=0.5; y=0.5)

A mixture of 0.030 mole of diol monomer (a), 0.030 mole of diethyleneglycol, 0.063 mole of toluene diisocyanates (mixture of 2,4- and2,6-diisocyanates), and 0.05 gram of dibutyltin dilaurate was dissolvedin 100 milliliters of dried dimethyl sulfoxide. The mixture was heatedunder an inert atmosphere at 70° to 75° C. for 4 hours, after which 5milliliters of ethanol were added. Thereafter, the reaction mixture washeated for another hour before cooling down to room temperature. Thismixture was then poured slowly into 3 liters of swirling methanol toprecipitate the resultant polyurethane. The polyurethane product wasfiltered and washed twice with 500 milliliters of methanol. The yield ofthe above copolyurethane (I) was 86 percent after drying in vacuo at 65°C. for 24 hours; DP (degree of polymerization) was 103; Tg 121° C.(mid-point); IR (KBr) 1,729; 2,221 cm⁻¹.

EXAMPLE V Synthesis of Copolyurethane (FIG. 1, x= 0.6; y=0.4)

Copolyurethane of FIG. 1 above was prepared according to the procedureof Example (IV) except that 0.036 mole of diol monomer (a), 0.024 moleof diethylene glycol, and 0.063 mole of toluene diisocyanates wereemployed; and the reaction was conducted for 6 hours. The yield was 88percent; DP 112; and Tg 134° C. IR (KBr) 1,730; 2,221 cm-¹.

EXAMPLE VI Synthesis of Copolyurethane (FIG. 3, x=0.5; y=0.5)

A mixture of 0.150 mole of diol monomer (a), 0.150 mole of t-butylbis(2-hydroxyethylamine), and 0.316 mole of tolylene diisocyanates, and0.2 gram of dibutyltin dilaurate in 700 milliliters of drieddimethylsulfoxide was heated under a nitrogen atmosphere at 70 to 75° C.for 10 hours. Subsequently, 10 milliliters of absolute ethanol was addedand the reaction was continued at the same temperature for another hour.After cooling down to room temperature, the reaction mixture was pouredinto 5 liters of methanol to precipitate the above polyurethane product.The precipitate was filtered, washed with methanol, and dried in vacuoat 60° C. for 24 hours. The yield of the above copolyurethane was 91percent; DP 121; and Tg 134° C.; IR (KBr) 1,730; 2,222 cm-¹.

EXAMPLE VII Synthesis of Copolyurethane (FIG. 4, x =0.5; y=0.5)

The synthesis of the above copolyurethane was accomplished in accordancewith the procedure of Example VI with a mixture of 0.030 mole of diolmonomer (a), 0.030 mole of 1,8-octanediol, 0.063 mole of toluenediisocyanates, and 0.05 gram of dibutyltin dilaurate. The yield of theabove copolyurethane was 84 percent; DP 99; Tg 118° C.; IR (KBr) 1,730;2,222 cm⁻¹.

EXAMPLE VIII Synthesis of Copolyurethane (FIG. 6, x=0.6 y=0.4)

The synthesis of copolyurethane was accomplished in accordance with theprocedure of Example IV with monomer (c), 1,5-pentanediol and toluenediisocyantes except that the reaction was conducted in drydimethylformamide. The yield of the above copolyurethane was 92 percent;DP 103; Tg 107° C.; Ir (KBr) 1,730; 2,222 cm⁻¹.

EXAMPLE IX Synthesis of Copolyurethane (FIG. 8, x=0.7; y=0.3)

The synthesis of the above copolyurethane was accomplished in accordancewith the procedure of Example V with 0.042 mole of diol monomer (b),0.018 mole of t-butyl bis(2-hydroxyethyl)amine, 0.063 mole of1,4-benzenediisocyanate, and 0.05 gram of dibutyltin dilaurate. Thereaction was conducted in dried tetrahydrofuran, and the yield of theabove copolyurethane was 87 percent; DP 89; Tg 138° C.; IR (KBr) 1,730;2,222 cm⁻¹.

EXAMPLE X

A photoresponsive imaging member comprising a nickel plate substratecoated with an alloy of selenium arsenic with 99.5 percent of selenium,and doped with 100 ppm of chlorine was overcoated with a layer ofcopolyurethane obtained from Example IV. The solution for theovercoating was prepared by dissolving 2.0 grams of copolyurethane in 35milliliters of tetrahydrofuran. This solution was coated over theselenium alloy layer by means of a Bird Film applicator. The coating wasthen dried in a forced air oven at 50° C. for 60 minutes, and anovercoat of a dry thickness of 2.0 microns was obtained. Subsequently,the fabricated photoresponsive imaging member was cooled to roomtemperature and electrically tested as follows:

The member was charged positively with corona, and discharged byexposing to white light of wavelengths of 400 to 700 nanometers.Charging was accomplished with a single wire corotron in which the wirewas contained in a grounded aluminum channel, and was strung between twoinsulating blocks. The acceptance potential of this imaging member aftercharging, and its residual potential after exposure were recorded. Theprocedure was repeated for different exposure energies supplied by a 75watt Xenon arc lamp of incident radiation, and the exposure energyrequired to discharge the surface potential of the member to half of itsoriginal value was determined. This surface potential was measured usinga wire loop probe contained in a shielded cylinder and placed directlyabove the photoreceptor member surface. This loop was capacitivelycoupled to the photoreceptor surface so that the voltage of the wireloop corresponds to the surface potential. Also, the cylinder enclosingthe wire loop was connected to the ground. For this imaging member, theacceptance potential was 1,200 volts, the residual potential was 100volts, and the half decay exposure sensitivity was 10 ergs/cm². Further,the electrical properties of this photoreceptor member were essentiallythe same after 1,000 cycles of repeated charging and discharging.Specifically, the electrical stability of the photoreceptor member wastested by monitoring the surface potentials for 1,000 cycles.Xerographic cycling is essentially the repetition of a photoinduceddischarge experiment for a specific number of cycles. Each photoinduceddischarge experiment constitutes a single cycle, and typically anindividual cycle will include charging, a dark decay period, exposure, adischarge period, and erasure by light of the remaining charge on thephotoreceptor surface.

EXAMPLE XI

Two substantially identical organic photoresponsive imaging members werefabricated by coating a charge transport layer of a thickness of 15microns on an aluminized Mylar substrate of a thickness of 50 microns.The transport layer was comprised of 50 percent ofN,N'-diphenyl-N,N'-bis(3-methylphenyl)benzidine dispersed in 50 percentby weight of Makrolon polycarbonate. Photogenerator layers, 0.5 micronin thickness, comprising 30 percent of vanadyl phthalocyanine dispersedin 70 percent by weight of polyester PE-100, available from Goodyear,were spray coated on the aforementioned transport using a commercialspray gun. One of these fabricated imaging members was overcoated with alayer of copolyurethane prepared in accordance with the procedure ofExample V. The thickness of the overcoat was 2 microns. The otherfabricated imaging member was not overcoated and served as a control.

These two devices were then tested electrically by positively chargingto a surface potential of about 950 volts, and discharging by exposingto 830 nanometers monochromatic light. The results indicated that bothdevices possessed a similar acceptance potential and similar exposuresensitivity. However, the overcoated device displayed a dramaticimprovement in its dark decay characteristics as compared to the controldevice as follows:

    ______________________________________                                                                     Half-Decay                                               Acceptance Dark      Exposure                                                 Potential  Decay     Sensitivity                                              (Volts)    (Volts/sec.)                                                                            (ergs/cm.sup.2)                                  ______________________________________                                        Control Device                                                                          950          200       15                                           Overcoated                                                                              950           45       15                                           Device                                                                        ______________________________________                                    

EXAMPLE XII

A photoresponsive imaging member was prepared by coating an aluminumdrum, 500 microns thick, with a photoconductive layer of an arsenicselenium alloy, 99.5 percent selenium doped with 100 parts of chlorine.This imaging member was then overcoated with a copolyurethaneovercoating by the spray coating technique as follows:

A solution for the overcoating was prepared by dissolving 6.0 grams ofcopolyurethane obtained from Example VI in 120 milliliters of methylenechloride and 80 milliliters of 1,1,2-trichloroethane. This solution wasspray coated onto the aforementioned photoresponsive imaging drum usinga commercial spray gun (Brinks Model 21) in a humidity andtemperature-controlled housing. The relative humidity was maintained at35 percent, and the temperature at 20° C. during spraying. Theovercoated drum was then dried in a forced air oven at 50° C. for 90minutes affording a 2.5 microns thick copolyurethane overcoating.

The overcoated drum thus obtained was subject to print testing in aXerox 2830^(R) copier at a relative humidity range of 20 percent to 70percent, and temperature range of 10° C. 30° C. A total of 30,000 copieswere produced from this overcoated imaging member. Several test patternswere used to monitor the image quality of the copies, which imagequality was excellent as evidenced by the high resolution with no imageblurring and no image deletion, and clean background. No visual defectson the polyurethane overcoating were detected.

EXAMPLE XIII

A photoresponsive imaging member comprising a ball grained aluminumplate of a thickness of 40 mils coated with a 60 microns thick layer ofa selenium tellurium alloy (75/25) was overcoated with a layer ofcopolyurethane obtained from Example VII as follows:

A solution for the overcoating was prepared by dissolving 4.0 grams ofthe above copolyurethane in 50 milliliters of methylene chloride. Thesolution was coated over the selenium-tellurium photoconductive layer bymeans of a Bird Film applicator. Subsequently, the coating was dried ina forced air oven at 50° C. for 30 minutes resulting in a thickness of1.5 microns. The overcoated photoresponsive imaging member waselectrically tested in accordance with the procedure of Example X, andsubstantially similar imaging results were obtained.

EXAMPLE XIV

A photoresponsive imaging member similar to that of Example XI with theexception that the ball grained aluminum plate of Example XIII wasselected. Specifically, a photogenerator layer comprising trigonalselenium and the diamine of Example XI dispersed inpoly(N-vinylcarbazole) was coated on top of the diamine transport layer.The thickness of the transport layer was 25 microns and that of thephotogenerator was 2 microns. An overcoat layer of the copolyurethaneobtained from Example VI was applied on top of the photogenerator layerby means of a Bird Film applicator. Electrical testing of this devicewas accomplished by repeating the procedure of Example X, andsubstantially similar results were obtained.

Although the invention has now been described with reference to specificpreferred embodiments, it is not intended to be limited thereto butrather those of ordinary skill in the art will recognize that variationsand modifications, including equivalents thereof, may be made thereinwhich are within the spirit of the invention and within the scope of theclaims.

What is claimed is:
 1. A process for the preparation of thecopolyurethanes of the formula: ##STR15## wherein A is a trivalentgroup; A' is a bivalent group selected from the group consisting ofalkylene and arylene; R is selected from the group consisting ofalkylene, substituted alkylene, arylene, and substituted arylene; x andy are number mole fractions of from about 0.05 to about 0.95 subsequentto the provision that the sum of x+y is equal to 1.0, which comprisesthe polycondensation of a dihydroxy-functionalized9-dicyanomethylenefluorene-4-carboxylate, a diol and a diisocyanate inthe presence of a catalyst and a suitable solvent; and wherein thereaction mixture is heated.
 2. The copolyurethanes of the formula##STR16## wherein A is a trivalent group; A' is a bivalent groupselected from the group consisting of alkylene and arylene; R isselected from the group consisting of alkylene, substituted alkylene,arylene, and substituted arylene; x and y are number mole fractions offrom about 0.05 to about 0.95 subsequent to the provision that the sumof x+y is equal to 1.0.
 3. A copolyurethane selected from the groupconsisting of those represented by the following formulas ##STR17##wherein x and y are number mole fractions of from about 0.05 to about0.95 wherein the sum of x+y is equal to 1.0, and t represents tertiary.4. A process for the preparation of copolyurethanes which comprises thepolycondensation of dihydroxy-functionalized9-dicyanomethylenefluorene-4-carboxylate, a diol and diisocyanate in thepresence of a catalyst and a suitable solvent; and wherein the reactionis affected at a temperature of from about 50° C. to about 80° C.
 5. Aprocess in accordance with claim 4 wherein the solvent is selected fromthe group consisting of dimethylsulfoxide, dimethylformamide,dimethylacetamide, tetrahydrofuran, dioxane, glyme, diglyme, andtriglyme.
 6. A process in accordance with claim 4 wherein the catalystis dibutyltin dilaurate.
 7. A process in accordance with claim 4 whereinthe dihydroxy compound is 2,2-bis(hydroxymethyl)butyl9-dicyanomethylenefluorene-4-carboxylate.
 8. A process in accordancewith claim 4 wherein the dihydroxy compound is2-[bis(2-hydroxyethyl)amino]ethyl9-dicyanomethylenefluorene-4-carboxylate.
 9. A process in accordancewith claim 4 wherein the diisocyanate is phenylene diisocyanate.
 10. Aprocess in accordance with claim 4 wherein the diisocyanate is tolylenediisocyanate.
 11. A process in accordance with claim 4 wherein thediisocyanate is 1,6-hexane diisocyanate.
 12. A process for thepreparation of the copolyurethane of the following formula ##STR18##wherein A is a trivalent group; A' is a bivalent group selected from thegroup consisting of alkylene and arylene; R is selected from the groupconsisting of alkylene, substituted alkylene, arylene, and substitutedarylene; x and y are number mole fractions of from about 0.05 to about0.95 subsequent to the provision that the sum of x+y is equal to 1.0,which comprises the polycondensation reaction of adihydroxy-functionalized monomer, a diol, and a diisocyanate in thepresence of a catalyst in a suitable solvent; and wherein the reactionmixture is heated to accomplish polymerization.